Assimilation of Feng-Yun-3B satellite microwave humidity sounder data over land

Abstract

The ECMWF has been assimilating Feng-Yun-3B (FY-3B) satellite microwave humidity sounder (MWHS) data over ocean in an operational forecasting system since 24 September 2014. It is more difficult, however, to assimilate microwave observations over land and sea ice than over the open ocean due to higher uncertainties in land surface temperature, surface emissivity and less effective cloud screening. We compare approaches in which the emissivity is retrieved dynamically from MWHS channel 1 [150 GHz (vertical polarization)] with the use of an evolving emissivity atlas from 89 GHz observations from the MWHS onboard NOAA and EUMETSAT satellites. The assimilation of the additional data over land improves the fit of short-range forecasts to other observations, notably ATMS (Advanced Technology Microwave Sounder) humidity channels, and the forecast impacts are mainly neutral to slightly positive over the first five days. The forecast impacts are better in boreal summer and the Southern Hemisphere. These results suggest that the techniques tested allow for effective assimilation of MWHS/FY-3B data over land.

摘要

欧洲中期天气预报中心于 2014 年 9 月 24 日起将风云三号 B 星微波湿度计海洋上空的观测资料正式投入业务预报系统使用. 而由于受到地表温度和地表发射率的较大偏差以及无效云检测的影响, 同化陆地和冰雪覆盖的地表上空的观测资料远比同化海洋上空的观测资料难. 我们将从风云三号 B 星微波湿度计通道 1(150赫兹)反演出来的动态地表发射率与从不同的 NOAA 和 EUMETSAT 卫星上的微波湿度计89 赫兹通道集成的地表发射率图谱进行了比较. 利用动态地表发射率同化风云三号 B 星微波湿度计陆地上空观测资料可减小 ATMS 等同等仪器的观测背景误差, 且五天内预报影响为中性到正效果. 北半球夏季和南半球的预报影响更好. 这些结论说明了利用动态地表发射率同化风云三号 B 星微波湿度计陆地上空的观测资料是积极有效的.